There's a screw under your seat on the left hand side, you'll know it when you see it. Use a 6" long phillips head and make sure you're at operating temp when you do it. Really easy.
It's not really "under" the tank but below it. Locate the black rubber isolator toward the rear of the tank on the left side. Go about 5" forward and it's located about 3" in between the tank and the frame. The adjustment screw is a phillips head.